Smooth top cookers such as stoves and the like have a flat sheet of, for example, a glass ceramic which forms the actual heating surface upon which a cooking utensil is placed and a heating unit which includes a heating element disposed below the glass ceramic sheet. The sheet must be capable of transferring the heat from the heating unit to the cooking utensil and of withstanding the very high temperatures without softening or cracking. Such designs have advantages of easy cleaning over cookers in which the cooking utensil is heated by direct radiation or direct contact with a heating element.
The electrical heating unit described in our U.K. Pat. No. 1,433,478 has proved extremely successful in practice and has been found to have a relatively high efficiency, a relatively short response time to temperature control adjustment and a long life. As described in that patent the heating element coil is held in its helical shape by staples which are anchored in a base layer of thermal and electrical insulation. In order to ensure adequate anchoring of the staples the insulation has to be quite thick, often more than would be necessary for thermal insulation purposes. Therefore the overall depth of the heating units shown in that patent is usually relatively large. This is not a problem in many designs of cooker but, where the smooth top cooking unit is combined into a design in which the electrical controls project under the edge of the stove, the overall depth of the heating units can be such that they may interfere with the electrical controls.
It is therefore an object of this invention to provide an electrical heating unit which can have a smaller overall depth.